An important advancement in aircraft flight safety has been the development of EGPWSs. These warning systems analyze the flight parameters of the aircraft and the terrain surrounding the aircraft. Based on the analysis, these warning systems provide alerts to the flight crew concerning possible inadvertent collisions with terrain or other obstacles. Further, these EGPWSs ensure, by providing an alert, that the pilot maintains a minimum altitude with regard to terrain underlying the aircraft. The RFCF maintains the aircraft at an appropriate altitude relative to the runway field elevation.
The EGPWS generates an RFCF envelope that provides minimum altitudes that the aircraft should maintain above the selected runway elevation as the aircraft approaches the runway for landing. If the altitude of the aircraft with respect to the selected runway elevation is less than the minimum altitude required by the RFCF envelope, the EGPWS will provide an appropriate alert.
FIG. 1 illustrates a typical RFCF envelope 110 generated by at least one EGPWS. The RFCF envelope 110 is typically generated with reference to a selected runway 112. For different distances from the selected runway 112, the RFCF envelope 110 prescribes different minimum altitudes that the aircraft should maintain above the selected runway elevation. An alert is provided if the aircraft intrudes within the RFCF envelope 110.
For example, if an aircraft is within 5 nm from the runway 112, the RFCF prescribes that the aircraft maintain at least an altitude of 300 feet above the runway elevation. As such, if the aircraft is flying an approach that has an elevation of 900 feet, the aircraft should maintain an altitude of at least 1200 feet. In this example, if the aircraft dips below 1200 feet altitude to the destination runway 112, the RFCF will provide an appropriate alert.
Importantly, with reference to FIG. 1, for distances closer to the selected runway 112, the RFCF envelope 110 requires smaller minimum clearance altitudes that the aircraft should maintain above the selected runway elevation. This portion 114 of the RFCF envelope 110 reflects a landing pattern of the aircraft. The altitudes at various distances from the selected runway 112 are selected to provide proximity warning protection, while also reducing generation of nuisance alarms that may disrupt the flight crew during landing. For example, when the aircraft is 4.5 nm from the selected runway, the flight crew will not receive an alert unless the aircraft dips to an altitude that is less than 300 feet above the runway elevation. The RFCF envelope 110 typically may be spaced 1.0 mile from the runway; however, preferably is 0.5 mile from the runway.
For most instances, the RFCF envelopes generated by the EGPWS, such as the RFCF envelope 110 illustrated in FIG. 1, are generally advantageous as they provide ground proximity warning protection, while at the same time reducing nuisance alarms. However, there may be specific flight profiles where improvements to the system may be made.
Specifically, as described above, the RFCF envelope 110 requires minimum altitudes that the aircraft should maintain above the selected runway depending upon the distance between the aircraft and the selected runway. While the RFCF envelope 110 is typically more than adequate for ground proximity warning protection, problems may occur when undesired flight profiles interfere with this protection.
Typically, the RFCF envelope 110 terminates a mile, as shown in FIG. 1, from the end of the runway. An undesired flight profile, for example, a steep descent, may place the aircraft in close proximity to the terrain within this mile without receiving an alert.
Accordingly, it is desirable to provide a system and method for modifying the RFCF envelope with regard to an undesired flight profile. Furthermore, other desirable features and characteristics of the exemplary embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.